The present invention relates to tubular prostheses such as grafts and endoluminal prostheses including, for example, stent-grafts and aneurysm exclusion devices, and methods for placement of such grafts and endoluminal structures. More particularly, the present invention relates to a graft or a prosthetic device including a graft constructed of monofilament fibers for placement within or in place of a body lumen, including, for example, vascular grafts for replacing blood vessels, devices for opening or supporting blood vessels, and devices for the treatment of abdominal and other aneurysms.
A wide range of medical treatments have been previously developed using xe2x80x9cendoluminal prostheses,xe2x80x9d which terms are herein intended to mean medical devices which are adapted for temporary or permanent implantation within a body lumen, including both naturally occurring or artificially made lumens. Examples of lumens in which endoluminal prostheses may be implanted include, without limitation: arteries such as those located within coronary, mesentery, peripheral, or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes. Various types of endoluminal prostheses have also been developed, each providing a uniquely beneficial structure to modify the mechanics of the targeted luminal wall.
Also a number of vascular grafts have been developed for either replacing, supplementing or excluding portions of blood vessels. These vascular grafts may include but are not limited to endoluminal vascular prostheses.
Graft materials have been used in a number of medical applications including in vascular graft and/or in endoluminal prostheses. Among other applications, materials have been used in tubular vascular prostheses for repairing or replacing blood vessels. They have also been used in aneurysm exclusion devices such as abdominal aortic aneurysm (xe2x80x9cAAAxe2x80x9d) devices that are used to exclude aneurysms and provide a prosthetic lumen for the flow of blood. Further uses have included stent-grafts such as covered stents that are used for providing artificial radial support to the wall tissue, which forms the various lumens in the body. Such covered stents have attempted among other things to address problems that are presented by a thrombogenic environment or to promote healing in the vessel wall tissue that is prone to scarring. These attempts include providing a lining or covering in conjunction with an implanted stent. Typically graft materials used in these include multifilament woven polymer materials and polytetrafluoroethylene (xe2x80x9cPTFExe2x80x9d). The stent-grafts may have graft material on the inner diameter or outer diameter of a support structure.
One very significant of these uses for endoluminal or vascular grafts is in treating aneurysms.
Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease or genetic predisposition which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aneurysms occurring in the abdominal aorta. Typically an abdominal aneurysm will begin below the renal arteries and may extend into one or both of the iliac arteries.
Aneurysms, especially abdominal aortic aneurysms, have been most commonly treated in open surgery procedures where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique in view of the alternative of a fatal ruptured abdominal aortic aneurysm, the open surgical technique suffers from a number of disadvantages. The surgical procedure is complex and requires long hospital stays due to serious complications and long recovery times and has high mortality rates.
In order to reduce the mortality rates, complications and duration of hospital stays, less invasive devices and techniques have been developed. The improved devices include tubular prostheses that provide a lumen or lumens for blood flow while excluding blood flow to the aneurysm site. The prostheses are typically made of a tubular multifilament woven graft material that is secured to a vessel wall above and below the aneurysm site with at least one attached expandable ring member that provides sufficient radial force so that the prosthesis engages the inner lumen wall of the body lumen. Other mechanisms have been used to engage the vessel walls such as, for example, forcibly expandable members or hook like members that puncture the vessel wall.
Although frequently referred to as stent-grafts, these devices differ from covered stents in that they are not used to mechanically prop open natural blood vessels. Rather, they are used to secure an artificial lumen to the vessel wall without further opening the natural blood vessel that is already abnormally dilated.
These aneurysm exclusion devices are preferably loaded into a catheter, which is used to deliver and place the prosthesis at an appropriate location. This has been done one of several ways. Most frequently, a surgical cut down is made to access a femoral iliac artery. The catheter is then inserted into the artery and guided to the aneurysm site using fluoroscopic imaging where the device is released from the catheter. Where expandable rings are used, the rings supporting the graft, biased in a radially outward direction, then expand to engage the prosthesis in the vessel against the vessel wall to provide an artificial lumen for the flow of blood. Another technique, though less frequently used, includes percutaneously accessing the blood vessel for catheter delivery, i.e., without a surgical cutdown.
Multifilament fibers have been used in AAA devices, primarily because it was believed that the fibers provide relative strength and durability required by the prostheses and monofilament fiber based grafts have been avoided because they had insufficient leak resistance. Typically the woven multifilament graft material is made of yarns which consist of about 25 to 100 fibers. The selection of yarn dictates the resultant mechanical properties such as percent elongation, fatigue strength, burst strength, and permeability to water or other fluids. One disadvantage to using these materials is that the multifilament fiber adds bulk, and relatively bulky grafts are more difficult to deliver using modem low-profile endovascular techniques. Another disadvantage is that they cannot be woven into fabric without a significant number of fissures or hooks (frays) and defects that occur during the weaving process. These fissures, hooks and defects tend to make the woven graft material even thicker and may cause increased tissue immune response. Lower profile multifilament woven materials have not provided sufficient strength to the grafts in which they have been used.
One disadvantage of the currently used devices is that when radially compressed, they are larger than would be ideal and thus require larger diameter catheters for delivery. This makes catheter access to the site and maneuverability through the tortuous or narrowed diseased vessels more difficult and may exclude some patients from eligibility for some procedures. In most current AAA devices, the total outer diameter of the introducer systems are relatively large, i.e., around 20-24 French. Providing a smaller introducer system would, among other things, allow for treatment of patients with smaller blood vessel diameters and provides for faster delivery.
Therefore, it is desirable to provide an endoluminal graft that is made of a material having sufficient strength, durability and low-permeability, while capable of being radially compressed into and delivered from smaller diameter delivery catheters.
The present invention provides an improved endoluminal prosthesis made of a graft material having a relatively smaller collapsed profile. In particular, the present invention provides an endoluminal graft device made of monofilament fibers instead of the fiber bundles of the multifilament fibers. Accordingly the present invention provides for a lower volume structure with comparable strength. More particularly, the graft material comprises a finely woven monofilament fiber with a small enough pore size and low enough percent open area to provide thin graft material with low permeability. The monofilament fibers may be woven in a number of ways as are generally known in the art to provide more densely packed material and smaller pore sizes. In one preferred embodiment, the material is woven polyester. The monofilament fibers may be shaped in a manner to provide a more compact and stronger material. For example, the fibers may be rounded or oval in shape.
The graft material is of a sufficiently low permeability so as to avoid excessive leakage, to prevent pressurization of the aneurysm and/or to form a seal. Although some leakage of blood or other body fluid may occur into the aneurysm site isolated by the prosthesis, the graft material is believed to prevent the pressurization of the aneurysm and thus aneurysm rupture. It is believed that by preventing excessive leakage into the aneurysm site the chance of pressurization of the aneurysm will be significantly decreased. In other words, by isolating the aneurysm from the flow of blood through the blood stream, aneurysm rupture is prevented. Permeability of the graft, in part, determines whether or not excessive or clinically undesirable leakage will occur through the graft material. Preferably the water permeability of the graft is at about 2300 ml/cm2/min or less and most preferably at about 600 ml/cm2/min or less.
Another important parameter in constructing a graft is the material thickness. The thickness of the material is sufficiently low to allow the endoluminal graft to collapse to a small enough profile to allow placement into the vasculature. The graft is thus thin-walled so that is may be compressed into a small diameter catheter, yet capable of acting as a strong, leak-resistant, fluid conduit when in tubular form. The present invention in the embodiment of an AAA device would enable smaller French size introducer systems, i.e., to sizes of 18 French or less. Preferably the wall thickness is in the range of 80 microns or less.
The strength of the material is sufficient to allow it to withstand the loads applied during deployment and the cyclical loading in the body for a reasonable duration. Where an annular support structure or stent is used, the endoluminal graft must provide sufficient strength to allow attachment of the annular support structure or the stent.
Preferably the graft material has a pore size of 11 microns or less, a percent open area of about 5% or less, and/or a tensile strength of about 44 pounds per inch, most preferably a pore size of about 5 micron or less, a percent open area of about 1% or less and a tensile strength of about 65 pounds per inch or less. A suitable material would be a polyester.
A preferred embodiment of the present invention relates to a tubular grafts constructed of monofilament fibers for endoluminal placement within a body lumens, including blood vessels, and for the treatment of abdominal and other aneurysms. This embodiment of the tubular graft includes radially compressible annular spring portions which when released, bias the proximal and distal portions of the graft into conforming fixed engagement with an interior surface of the vessel.
One embodiment provides an aneurysm repair system characterized by a graft apparatus which can be placed within a diseased vessel via deployment means at the location of an aneurysm. The graft device comprises a tubular graft formed of a woven monofilament fiber for conducting fluid. The graft device may be in the form of either a straight single-limb graft or a generally Y-shaped bifurcated graft having a trunk joining at a graft junction with a pair of lateral limbs, namely an ipsilateral limb and a contralateral limb. Preferably the ipsilateral limb is longer so that when deployed, it extends into the common iliac. A single limb extension graft is provided having a mating portion for coupling with a lateral limb of a bifurcated graft and an adjustable length portion extending coaxially from a distal end of the mating portion.
The graft apparatus includes radially compressible spring means having at least two coaxially spaced annular portions for biasing the proximal and distal portion of an associated graft limb or limb portion radially outward into conforming fixed engagement with the interior of the vessel. The annular portions are preferably constructed of nitinol. Examples of such spring means are described, for example, in U.S. Pat. Nos. 5,713,917 and 5,824,041 incorporated herein by reference.
In the extension graft, an annular spring portion is located at a distal end of the adjustable length portion for similar biasing purposes. The proximal portion of the extension graft includes a spring means for engaging the inner lumen of the contralateral limb portion of the graft.
The spring means may be attached to the graft by various means, such as, for example, by stitching the annular portions on either the inside or outside of the tubular graft.
Various means for deployment of the devices are well known in the art and may be found for example is U.S. Pat. Nos. 5,713,917 and 5,824,041 which are incorporated herein by reference. In general, the graft is radially compressed and loaded into a catheter. The aneurysm site is located using an imaging technique such as fluoroscopy and is guided through a femoral iliac artery with the use of a guide wire to the aneurysm site. Once appropriately located, the sheath on the catheter covering the tubular graft is retracted, thus allowing the annular springs to expand and attach or engage the tubular graft to the inner wall of the body lumen.